Insight into the Factors for Separation of Lignin and Cellulose by Ionic Liquids Based on Molecular Simulation

It is reported that many kinds of biomass can be dissolved in a variety of ionic liquids. However, the separation mechanism of biomass has not been studied deeply enough. In this work, the separation mechanism of lignin and cellulose in ionic liquids (ILs) was studied by molecular dynamics simulation. In order to define the separation effect of ILs on lignin and cellulose, it is characterized by two factors: separation speed and separation capacity, which, respectively, correspond to the dynamics and thermodynamics of the system. In this work, the relative separation factor and the relative diffusion factor are proposed, which together determine the separation effect of lignin and cellulose in ILs. In this work, 1-butyl-3-methylimidazolium acetate [Bmim][OAc], 1-ethyl-3-methylimidazolium acetate [Emim][OAc], 1-ethyl-3-methylimidazolium glycine [Emim][Gly], choline glycine [Choline][Gly], and choline acetate [Choline][OAc] were selected as solvents. The simulation results show that the separation speed and separation capacity are significantly different in the [Choline][Gly] system as well as the structure and H-bond changes. The differences are conducive to the separation of lignin and cellulose. This study provides insights into the separation of biomass and application of ILs.